Visual Beat - Interactive music video
EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
stats.fm - With the click of a button you'll be logged with your Spotify account and you'll instantly gain access to a valhalla of cool stats and insights.
GNU Solfege - GNU Solfege is free music education software.
SoundViz - Turn music and sounds into beautiful art
LenMus - LenMus is a free program for learning music.